This invention relates to the tinting or coloring of a hydrogel contact lens or other opthalmic prosthetic device, and refers more particularly to the opaquing procedure to which the lens is subjected prior to application of a specific tint or coloration to the lens.
Contact lenses can be tinted for cosmetic appearance as well as to reduce light transmission thereby providing the wearer with increased visual comfort. It is, of course, important that the tinted, or colored, lens impart a natural appearance to the wearer's eye. A natural-appearing soft contact lens should have a clear central or pupil area, a tinted intermediate or iris area and a clear outer area so that the tinted portion will not cover the sclera of the eye. Moreover, the central portion of the lens should be untinted to permit maximum light passage into the eye interior
U.S. Pat. No. 4,518,390 discloses a method and apparatus with which a contact lens can be tinted. However, lenses tinted in accordance with the teaching of the '390 patent are generally limited to use by individuals having light colored eyes. For individuals with dark irises, i.e., brown eyes, a change in color is obtained only with the darkest of lens tints as the underlying color of the iris tends to dominate the overall color effect. Such eyes can only be made to appear darker, not lighter.
U.S. Pat. No. 4,634,449 discloses a method by which lenses can be tinted to provide a variety of desired color effects, whether for cosmetic reasons or otherwise, which are unimpaired by, and independent of, the color of the wearer's eyes, i e., the visual effect of the tint is not appreciably influenced or modified by the color of the wearer's eyes. This is effected by first treating a hydrogel contact lens with an opaquing of selected areas of the lens, followed by tinting of the opaqued areas with a suitable tinting agent such as a water-soluble leuco ester of a vat dye. The initial opaquing can be achieved using a variety of chemical techniques, e.g., as described in U.S. Pat. No. 3,679,504.
Both U.S. Pat. No. 4,634,449 and U.S. Pat. No. 4,518,390 mount a lens of conventional circular profile in a holder which includes means for masking a central portion and a peripheral portion of the lens anterior surface so that these surfaces are unaffected during the opaquing and tinting operations and remain clear. An annular-shaped portion of the lens anterior surface intervening the central and peripheral portions communicates with a chamber in the holder apparatus. Opaquing medium present in the chamber contacts this annular-shaped portion causing it to become opaque. Thereafter, a tinting medium (with the opaqued lens mounted in the same or a like holder) is brought into contact with the entire opaqued portion of the lens surface. Due to its opaqued, tinted portion, which corresponds to the iris of the eye, the lens of U.S. Pat. No. 4,634,449 has a general uniformity of appearance or coloration which gives a certain impression of artificiality to the lens. In other words, in lacking variation in the coloring of the opaque portion and striae as are found in the natural iris, the lens can be less natural and cosmetically appealing when worn by an individual.